1. Field of the Invention
The present invention relates to positive temperature coefficient thermistors preferably for use in demagnetizing circuits included in electric appliances such as color television sets. More particularly, the present invention relates to positive temperature coefficient thermistors, in each of which a positive temperature coefficient thermistor element supported by metal terminals is included in a case and portions of the metal terminals extend outside of the case.
2. Description of the Related Art
FIG. 6 shows a positive temperature coefficient thermistor of the two-terminal type as an example of the related art. In this positive temperature coefficient thermistor, a positive temperature coefficient thermistor element 22 is supported by a pair of metal terminals 23a and 23b and is contained in a plastic case 21.
The case 21 includes a main body 24 having an open top portion and a cover member 25 attached to an opening 24a of the main body 24.
The metal terminals 23a and 23b are formed from a metal plate having a spring-like property. As shown in FIGS. 6 and 7, the metal terminals 23a and 23b include two springs 26a and 26b supporting the positive temperature coefficient thermistor element 22 interposed therebetween, supporting members 27a and 27b supporting the springs 26a and 26b, and connecting terminals 28 extending from the supporting members 27a and 27b. One end of each connecting terminal 28 passes through each slit 24b formed in the bottom of the main body 24 so as to extend outside the case 21.
In the metal terminals 23a and 23b, the springs 26a and 26b are supported by the two supporting members 27a and 27b disposed at each side, as shown in FIG. 7.
Additionally, the metal terminals 23a and 23b have the following arrangements:
(1) The supporting members 27a and 27b securely support the springs 26a and 26b so that the springs 26a and 26b can securely support the positive temperature coefficient thermistor element 22 interposed therebetween.
(2) Widths W1 and W2 of the springs 26a and 26b are set appropriately and a total value of widths W3 and W4 of the supporting members 27a and 27b is larger than a total value of the widths W1 and W2 of the springs 26a and 26b. With this arrangement, the springs 26a and 26b can have necessary spring thrusting forces and portions of the springs 26a and 26b in contact with the positive temperature coefficient thermistor element 22 have sufficient current capacity.
In this case, the widths W1 and W2 of the springs 26a and 26b are 1.5 mm and the widths W3 and W4 of the supporting members 27a and 27b are 1.9 mm.
When the total value of the widths W3 and W4 of the supporting members 27a and 27b is smaller than the total value of the widths W1 and W2 of the springs 26a and 26b, the supporting members 27a and 27b are deformed near the base ends of the springs due to the thrusting forces of the springs 26a and 26b. Consequently, satisfactory spring characteristics cannot be obtained. In addition, when the widths W1 and W2 of the springs 26a and 26b are too narrow, it is impossible to obtain both the necessary spring thrusting force and the current capacity of the portions of the springs 26a and 26 in contact with the positive temperature coefficient thermistor element 22.
Recently, there has been a growing demand for cost reduction in electric apparatuses. With this tendency, there has also been a strong demand for cost reduction in demagnetizing positive temperature coefficient thermistors used in electric apparatuses such as color television sets. In order to meet these demands, the sizes of metal terminals defining positive temperature coefficient thermistors and the cost thereof need to be reduced. However, for the reasons described above, it is difficult to miniaturize the metal terminals, with the result that cost reduction in such a positive temperature coefficient thermistor cannot be sufficiently achieved.
As another example of the related art, FIG. 8 shows a positive temperature coefficient thermistor of the three-terminal type, which includes two positive temperature coefficient thermistor elements 22a and 22b and a planar terminal 29 disposed therebetween. The positive temperature coefficient thermistor has the same problems as those shown in the positive temperature coefficient thermistor of the two-terminal type described above. In FIG. 8, elements having the same reference numerals as those used in FIGS. 6 and 7 represent the same or equivalent parts shown in FIGS. 6 and 7.
In order to overcome the problems described above, preferred embodiments of the present invention provide a highly compact and very inexpensive positive temperature coefficient thermistor including miniaturized metal terminals while maintaining the characteristics and reliability of the device.
According to one preferred embodiment of the present invention, a positive temperature coefficient thermistor includes a positive temperature coefficient thermistor element, a case including a main body having an open top portion and construct to house the positive temperature coefficient thermistor element and a cover member arranged to cover the open top portion of the main body, and at least one pair of metal terminals including springs downwardly extending from connecting portions at the upper ends of the springs to be kept in contact with the positive temperature coefficient thermistor element by spring thrusting forces so as to obtain electrical continuity to the element and supporting the positive temperature coefficient thermistor element interposed between the springs to retain the positive temperature coefficient thermistor element inside the case, supporting members having upper ends that are integrated with the connecting portions to support the springs, and connecting terminals arranged to extend through slits provided in the bottom of the case and so as to extend outside the case. In this positive temperature coefficient thermistor according to this preferred embodiment, a total width value of the supporting members is preferably smaller than a total width value of the springs and the connecting portions at the upper ends of the springs engage with one of the main body and the cover member so that the connecting portions are retained at predetermined positions.
As described above, the metal terminals have the springs supporting the positive temperature coefficient thermistor element interposed therebetween, at least one supporting member supporting each of the springs, and the connecting terminals passing through the slits formed in the bottom of the main body of the case so as to extend outside the case. Additionally, the total width value of the supporting members is preferably smaller than the total width value of the springs. Additionally, the connecting portions at the upper ends of the metal terminals engage with the main body or the cover member to be retained at the predetermined positions. With this arrangement, deformation of the supporting members is reliably prevented. Thus, the metal terminals can be miniaturized without sacrificing the reliability required when retaining the positive temperature coefficient thermistor element and the reliability of electrical continuity to the positive temperature coefficient thermistor element. As a result, the entire positive temperature coefficient thermistor can be produced at much lower cost.
In other words, in the positive temperature coefficient thermistor according to preferred embodiments of the present invention, the connecting portions at the upper ends of the metal terminals engage with the main body or the cover member to be retained at predetermined positions. Accordingly, even when the metal terminals are miniaturized by setting the widths of the supporting members to be smaller than the widths of the springs, deformation of the supporting members is reliably prevented. Thus, since the supporting members can support the springs securely, the reliability required when supporting the positive temperature coefficient thermistor element, the reliability of electrical continuity to the positive temperature coefficient thermistor element, and the current capacity of contacting portions can be securely obtained.
In addition, in this positive temperature coefficient thermistor according to another preferred embodiment of the present invention, the connecting portions of the metal terminals preferably engage with the main body or the cover member to be retained in the predetermined positions. Thus, for example, when compared with the case in which the supporting members of the metal terminals are insert-molded inside the main body, the entire structure of the device and its manufacturing process is greatly simplified. Accordingly, in this respect, also, further cost reduction can be achieved.
In terms of the positive temperature coefficient thermistor, when there are provided a plurality of supporting members and a plurality of springs, the total width value of the supporting members and the total width value of the springs are equivalent to a sum of the widths of the plurality of the supporting members and a sum of the widths of the plurality of the springs. When there is provided a single supporting member and a single spring, the total width is equivalent to each of the width of the single supporting member and the width of the springs.
Furthermore, in the positive temperature coefficient thermistor of preferred embodiments of the present invention, each of the metal terminals may include two or more springs and supporting members that are fewer in number than the springs.
With this arrangement, the metal terminals can be sufficiently miniaturized. Furthermore, when each of the metal terminals has two or more springs, the reliability required when retaining the positive temperature coefficient thermistor element and the reliability of electrical continuity to the positive temperature coefficient thermistor element can be maintained without fail.
In addition, alternatively, in this positive temperature coefficient thermistor, while using the equal numbers of the springs and the supporting members, the total width value of the supporting members may be preferably smaller than the total width value of the springs.
Furthermore, each of the metal terminals may be preferably formed by stamping out a metal plate having a spring-like property.
When using the metal terminals formed of such a metal plate, the positive temperature coefficient thermistor can obtain the reliability required when retaining the positive temperature coefficient thermistor element and the reliability of electrical continuity to the positive temperature coefficient thermistor element at low cost. Thus, even more advantages can be achieved with preferred embodiments of the present invention.
Furthermore, the positive temperature coefficient thermistor element may be a demagnetizing positive temperature coefficient thermistor element for use in, for example, a demagnetizing circuit.
Such a demagnetizing positive temperature coefficient thermistor included in a demagnetization circuit is usually incorporated in a home electronic apparatus such as a color television set. Thus, cost reduction in the demagnetizing positive temperature coefficient thermistors is more strongly demanded. With the use of a demagnetizing positive temperature coefficient thermistor according to preferred embodiments of the present invention, the positive temperature coefficient thermistor can be produced at very low cost without sacrificing the reliability of the device.
Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.